The present invention relates to the earth boring art and more particularly to a welding system for welding a multiplicity of individual segments together to form a rock bit.
A rotary rock bit in general consists of a main bit body adapted to be connected to a rotary drill string. Cutter means connected to the main bit body contact the formation during the drilling operation to form the desired borehole. The present invention provides a positioning fixture for clamping individual segments of the bit body together in the proper position for the final assembled bit and aligning the seams between segments with a beam of energy from a welding gun. Relatative movement between the segments and the beam causes the beam to traverse the seams in the plane of the seams and fuse the segments together.
The rotary rock bit must operate under extremely harsh environmental conditions and must effectively disintegrate very hard formations to produce the desired borehole. The gage size of the bits must be precise. Variation in the gage size of bits has been a problem in the prior art. In some operations the bit must pass through casing with a minimum clearance. In other operations it is necessary for the bit to pass through bored and still open holes which may be within a few thousandths of an inch of the gage size of the bit. If the gage size of the bits varies during the manufacturing process, the bits will encounter problems during the drilling operation.
The prior art methods of manufacturing rotary rock bits require the use of shims to size the bits to the proper gage size. The present invention allows the bits to be manufactured with an accurate and uniform gage size without the use of shims. During the construction of a prior art rotary rock bit a substantial amount of heat was generated when the separate segments of the bit were welded together. It was necessary to cool the bits to prevent tempering of steel components and heat damage to rubber components. The excessive heat could result in a change in temper of the metal of the rock bit, thereby creating the danger of a premature failure of the metal during the drilling operation. Since the rock bit often includes rubber or synthetic parts, any excessive heating in the vicinity of said parts could cause a weakening or destruction of said parts. It was necessary to use dowels between the segments of prior art bits to maintain the segments in the proper relationship during the welding operation.
The prior art method of manufacturing rotary rock bits consists of forming a weld groove between adjacent segments of the bit and filling the weld groove with a weld deposit by a welding process. Surfaces on adjoining segments are in adjacent relationship but the surfaces are not joined together and the joining of the segments is through the weld deposit. The cross sectional shape of the prior art weld was an irregular many sided polygon. An excessive amount of weld deposit was produced during the welding of prior art bits and the excessive amount of weld deposit would often result in warpage of the bit body. The excessive weld deposit also created the danger of the lubrication system and the bearing systems being contaminated during the manufacturing process by debris from the welding process. The weld deposit is not as hard as the body segments, thereby creating fatigue problems.
When the individual segments of the bit body are to be joined together, they must be accurately positioned during the welding process. If the individual segments are not properly positioned, the gage size of the bit will not be accurate. The prior art bits were checked for proper gage size by two ring gauges. If the gage size fell between the maximum ring gauge and the minimum ring gauge, the bit was considered satisfactory. It will be appreciated that such prior art bits would not have uniformly precise gage sizes. When a beam of energy is used to join the individual segments of the bit, the individual segments must be accurately aligned with the beam during the welding process. The joining of the individual segments of the bit body together in accordance with the present invention insures that the gage size of the bit will be uniformly accurate.
An illustration of the problems created with prior art manufacturing processes will be presented with reference to a rotary cone rock bit. A rotary cone rock bit includes at least one rotatable cutter mounted on a bearing pin extending from the main bit body. Bearings are provided between the cutter and the bearing pin to promote rotation of the cutter and means are provided on the outer surface of the cutter for disintegrating the formations as the bit and cutter rotate and move through the formation. A sufficient supply of lubricant must be provided to the bearings throughout the lifetime of the bit. The lubricant is maintained within the bearing area by a flexible rubber seal between the cutter and the bearing pin. Any excessive heating of the bit will damage the rubber seal and/or the lubricant. If the bit body is not constructed to a precise gage size, the bits will encounter difficulties when they are moved through casing having a minimum clearance or through a borehole with minimum clearance. Excessive weld deposits may result in warpage of the bit and a resulting inaccurate gage size.